Piezoelectric response induced by rotating the polarization, which occurs when the external field is not in the same direction as the internal spontaneous polarization, is studied using a first-principles approach. The piezo-response of the rhombohedralBaTiO3to the field along the ⟨001⟩ direction is considered. The response is found to be path-dependent, and along the lowest free-energy path the strain increases significantly with the field. Furthermore, the strain response (collinear response) to a field along the polarization direction (i.e., without polarization rotation) is also calculated for comparison, and the piezo-responses with and without rotating polarization are found to be very different. ©2000 American Institute of Physics.